1. Field of the Invention
The present invention relates to an electrophotographic recording apparatus based on electrostatic recording.
2. Description of the Related Art
In electrophotographic recording apparatuses of this type, information on an original document or the like is temporarily recorded as an electrostatic image on a photoreceptor drum, and the image is transferred to a recording sheet to record the information thereon. Initially, the surface of the drum is uniformly charged by means of a charger, and light is applied to the charged drum surface to remove electric charge thereon, thereby forming a charge image, in accordance with the information to be recorded. Then, a toner supplied from a developing unit is adhered to the charge image, thereby forming a toner image. In the meantime, a recording sheet is taken out from a paper cassette, and is delivered to a region between the photoreceptor drum, having the toner image thereon, and a transfer unit. Then, the sheet is electrostatically attracted to the drum by electric discharge from the transfer unit, and the toner image on the drum surface is transferred to the sheet. Subsequently, the recording sheet, having the toner image thereon, is heated by means of a fixing unit so that the toner is melted to fix the image on the sheet. On the other hand, the residual toner on the surface of the photoreceptor drum is removed by means of a cleaner to provide for the next cycle of recording.
Among the electrophotographic recording apparatuses arranged in this manner, some newly developed ones have a small auxiliary roller located just short of the photoreceptor drum, whereby the recording sheet can be brought more intimately into contact with the drum and the feed of the sheet is facilitated. Conventionally, in the apparatuses of this type, the transfer unit is disposed under the photoreceptor drum, aligning rollers are arranged on the upstream side of the drum with respect to the feeding direction of the recording sheet P, and a guide is interposed between the drum and the aligning rollers. The auxiliary roller 40 is situated between the guide and the transfer unit. A gear, which is in mesh with a gear on the photoreceptor drum, is provided on one end portion of the auxiliary roller. Also, a gear is provided on one end portion of one of the aligning rollers. Both these gears engage with a gear of a drive unit for rotation so that the photoreceptor drum, auxiliary roller, and aligning rollers rotate in association with one another.
Many of these recording apparatuses are of the clamshell type. The clamshell type is a type in which the apparatus housing comprises a lower casing and an upper casing swingably mounted thereon. In case of trouble, such as paper jamming, the upper casing can be swung open to give access to the internal mechanism to be inspected. Generally, in the clamshell-type recording apparatuses, a photoreceptor drum, charger, optical unit, developing unit, etc. are attached to the upper casing, and an auxiliary roller, transfer unit, etc. to the lower casing. It is to be desired that these members should be arranged in optimum positional relationships, in order to obtain satisfactory record images.
In the clamshell-type apparatuses, there are no special problems on the relative positions of members attached to a common body. The critical issue is the positional relationships between the members attached to the upper casing and the ones attached to the lower casing. It is difficult, however, to locate these members in optimum relative positions and maintain the optimum relationships. Since these relationships depend indirectly on the relative positions of the upper and lower positions joined together, they often vary from apparatus to apparatus due to assembly errors. In some cases, moreover, play at a bearing portion for supporting the upper casing may cause changes in the relative positions of the upper and lower casings, that is, in the respective positions of the transfer unit and the auxiliary roller relative to the photoreceptor drum. These variations or changes are undesirable negative factors for a technical object to provide fine-quality record images with stability.